FIG. 1 illustrates a schematic diagram of an existing Long Term Evolution (LTE) system which supports the relay node (RN).
In the wireless access network of the LTE system, the wireless resource management entity includes a macro base station (i.e., evolved Node B (eNB)) 101 and a RN 102 which is connected with a core network through another macro base station (i.e., Donor eNB (DeNB)) 103. The eNB 101 and DeNB 103 are connected each other via an X2 interface, and each eNB 101 is connected with a Mobile Management Entity (MME)/Servicing GateWay (S-GW) 104 in the core network through an S1 interface, respectively. The RN 102 accesses the DeNB 103 via an Un interface. The DeNB 103 provides an X2 proxy function between the RN 102 and other eNBs. The DeNB 103 provides an S1 proxy function between the RN 102 and the MME/S-GW 104. The S1 and X2 proxy functionality includes passing UE-dedicated S1 and X2 signaling between the RN 102 and the eNB 101, between the RN 102 and the MME 104, and between the RN 102 and the S-GW 104.
The currently defined relay is used in a fixed position, and does not support mobility of the relay between different cells. What is currently considered is how to apply the relay in a fast-moving train, for example in a train with a movement speed of 250-350 km per hour, and the wireless environment of the fast-moving train is rather special, for example, high noise, high penetration loss, serious Doppler frequency shift, and so on. The service quality provided by the existing relay cannot meet the needs of the operators, while the mobile relay is to solve the problems existing in the existing relay, to improve the quality of the service which can be provided in the fast-moving train to better meet the needs of users.
In the existing LTE system, when a User Equipment (UE) enters a cell and a Tracking Area Identifier (TAI) to which the cell belongs is not in a TAI list stored in the UE, the UE initiates a normal Tracking Area Update (TAU) process.
FIG. 2 illustrates a procedure for performing TAU process of the UE in the existing LTE system.
Step 201: a UE sends a TAU request message to an eNB. The UE sends the TAU request to the eNB through a Radio Resource Control (RRC) messages.
Step 202: the eNB sends the TAU request to an MME through an S1 message.
Step 203: the MME (i.e., new MME) obtains an old MME address according to a Globally Unique Temporary Identifier (GUTI) received from the UE. The new MME sends a context request message to the old MME to request for context information of the UE.
Step 204: the old MME sends context response message including context information of the UE to the MME.
Step 205: an authentication/certification process for the UE is implemented. This process is an optional step, is implemented only in certain circumstances.
Step 206: the MME sends a context confirmation message to the old MME.
Step 207: the MME sends a modify bearer request message to a S-GW/PDN GW.
Here, the detailed description of steps between the S-GW and PDN GW are omitted.
Step 208: the S-GW/PDN GW sends a modify bearer response message to the MME.
Step 209: the MME sends an update location request to a Home Subscriber Server (HSS).
Step 210: the HSS sends cancel location message to the old MME.
Step 211: the old MME sends a cancel location confirmation message to an old HSS.
Step 212: the HSS sends an update location confirmation message to the MME.
Step 213: the MME sends a TAU accept message to the UE.
Step 214: if the GUTI changes, the UE sends a TAU complete message to the MME to confirm to accept the new GUTI.